1 62 Introduction to Botany. 



DISCUSSION. 



116. Different Methods of Reproduction. The reproduc- 

 tion of plants may take place either asexually or sexually. 

 In the former process a greater or less portion of the 

 parent plant becomes detached, and grows to be an inde- 

 pendent individual. With some instances of this kind we 

 are already familiar. The reproduction of the potato by 

 means of tubers, of the sweet potato by means of roots, 

 and artificial reproduction by means of cuttings and grafts 

 have already been discussed in the chapters on stems and 

 roots. We have seen that portions of stems and roots, 

 and aggregations of stems and leaves in the form of 

 buds, as seen in the bulb of the onion, for instance, may 

 serve the purpose of reproduction. In some of the lower 

 forms of plant life a single cell may serve the same 

 purpose'. 



117. Reproduction in Ulothrix. In Ulothrix zonata (see 

 Fig. 85), a fresh-water Alga, the protoplasts of the cells 

 which constitute the body of the plant may divide to form 

 many daughter protoplasts, which break out from the 

 mother cell and swim about in the water by means of four 

 cilia; after a time these motile spores come to rest, and 

 each gives rise, by cell division, to a multicellular plant 

 body similar to the one from which it sprang. In the 

 same plant another process of reproduction may also take 

 place. A protoplast of one of the cells of the plant body 

 may divide to form daughter protoplasts smaller than those 

 just described, and having two cilia instead of four. These 

 swim about in the water for a time, but finally fuse in pairs 

 to form a spore, which by cell division and enlargement 

 produces a plant like the parent. The fusing daughter 

 protoplasts, or cells, as we may call them, may be considered 



